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Biomedical subjects

H Lai

Publications and source records attributed to H Lai.

At least 109 records · Page 6Linked to original sources
PubMed1987

Effects of low-level microwave irradiation on hippocampal and frontal cortical choline uptake are classically conditionable.

In previous research, we found that sodium-dependent high-affinity choline uptake in the hippocampus and frontal cortex of the rat was lowered after acute (45 min) exposure to low-level 2450-MHz pulsed microwaves (power density 1 mW/cm2; average whole body specific absorption rate, 0.6 W/kg; 2 mu sec pulses, 500 pps). In the present experiment, we investigated developments of tolerance and classical conditioning to these effects of microwaves. Rats were exposed to microwaves in cylindrical waveguides in 10 daily sessions (45 min per session). In an 11th session, we subjected the rats to either microwave (study of tolerance) or sham exposure (study of conditioned effect) for 45 min, and immediately measured choline uptake in the hippocampus and frontal cortex. We found that tolerance, a decrease in response to microwaves, developed to the effect of microwaves on choline uptake in the hippocampus, but not in the frontal cortex. Conditioned effects were also observed: an increase in choline uptake in the hippocampus and a decrease in uptake in the frontal cortex. These data suggest that the effects of microwaves on choline uptake in the hippocampus and frontal cortex are classically conditionable, probably to cues in the exposure environment.

Animals↗
PubMed1987

Acute exposure to noise affects sodium-dependent high-affinity choline uptake in the central nervous system of the rat.

Rats were acutely (45 min) exposed to white noise at intensity of either 70 or 100 dB. Sodium-dependent high-affinity choline uptake was determined in the striatum, frontal cortex, hypothalamus, and hippocampus immediately after exposure. The effects of noise on choline uptake varied according to the intensity of the noise and the brain area studied. Exposure to noise of 70 dB significantly increased the choline uptake in the frontal cortex, hypothalamus, and hippocampus as compared to the uptake of sham-exposed rats, whereas decreased choline uptake in the frontal cortex and hippocampus was observed acute exposure to noise of 100 dB. No significant effect on choline uptake in the striatum was seen after exposure to noise of either intensity. In addition, pretreatment of the rats with the narcotic antagonist naltrexone (1 mg/kg, IP) before noise exposure blocked the effects of noise on choline uptake in the central nervous system. Changes in cholinergic activity in the central nervous system could be a response to the stress effect of noise and may be mediated by endogenous opioids.

Animals↗
PubMed1987

Effects of intraseptal drug administration on pentobarbital-induced narcosis and hippocampal choline uptake.

Effects of injection of drugs into the septum on pentobarbital anesthesia were investigated in the rat. Intraseptal microinjection of bicuculline (5 micrograms), arecoline (2 micrograms), and phenylephrine (5 micrograms) shortened, MK-212 (5 micrograms) prolonged, and atropine (2 micrograms) had no significant effect on the duration of pentobarbital-induced loss of righting reflex. Bicuculline and arecoline increased and MK-212 reduced hippocampal cholinergic activity as measured by change in hippocampal sodium-dependent high-affinity choline uptake after intraseptal drug injection. It is concluded that activation of the septal-hippocampal cholinergic pathway might be an important neuromechanism for recovery from pentobarbital-narcosis.

Animals↗
PubMed1987

Low-level microwave irradiations affect central cholinergic activity in the rat.

Sodium-dependent high-affinity choline uptake was measured in various regions of the brains of rats irradiated for 45 min with either pulsed or continuous-wave low-level microwaves (2,450 MHz; power density, 1 mW/cm2; average whole-body specific absorption rate, 0.6 W/kg). Pulsed microwave irradiation (2-microseconds pulses, 500 pulses/s) decreased choline uptake in the hippocampus and frontal cortex but had no significant effect on the hypothalamus, striatum, and inferior colliculus. Pretreatment with a narcotic antagonist (naloxone or naltrexone; 1 mg/kg i.p.) blocked the effect of pulsed microwaves on hippocampal choline uptake but did not significantly alter the effect on the frontal cortex. Irradiation with continuous-wave microwaves did not significantly affect choline uptake in the hippocampus, striatum, and hypothalamus but decreased the uptake in the frontal cortex. The effect on the frontal cortex was not altered by pretreatment with narcotic antagonist. These data suggest that exposure to low-level pulsed or continuous-wave microwaves leads to changes in cholinergic functions in the brain.

Animals↗
PubMed1986

Sodium-dependent, high-affinity choline uptake in hippocampus and frontal cortex of the rat affected by acute restraint stress.

Acute (45-min) restraint stress decreased sodium-dependent, high-affinity choline uptake in the hippocampus and frontal cortex of rats. The effect of restraint on the hippocampus was blocked, whereas that on the frontal cortex was not significantly affected, by pretreatment of the rats with the narcotic antagonist naltrexone (1 mg/kg, i.p.) immediately prior to restraint.

Animals↗
PubMed1986

Effects of low-level microwave irradiation on amphetamine hyperthermia are blockable by naloxone and classically conditionable.

In a series of experiments, we investigated the effects of pulsed low-level microwave irradiation on amphetamine-induced hyperthermia in the rat. Rats were irradiated in a 2,450-MHz cylindrical waveguide exposure system at 1 mW/cm2, 2 mus pulses, 500 pps, average SAR of 0.6 W/kg. Acute (45 min) exposure to microwaves attenuated amphetamine-induced hyperthermia. This effect was blocked by pretreatment of the animals with the narcotic antagonist naloxone. In another experiment, rats were subjected to ten daily sessions of microwave exposure (45 min/session). On day 11, amphetamine-induced hyperthermia was studied in the animals immediately after a session of either microwave or sham exposure. Similar to the acute effect, amphetamine-induced hyperthermia was attenuated in rats irradiated with microwaves (unconditioned effect). In the sham-irradiated animals we observed a potentiation of the amphetamine-induced hyperthermia, which was a conditioned effect of microwaves. Thus, the conditioned effect (potentiation) was opposite in direction to the unconditioned effect (attenuation). No tolerance developed to the unconditioned effect after subchronic exposure. Furthermore, both conditioned and unconditioned effects of microwaves on amphetamine-induced hyperthermia could be blocked by treatment with naloxone. These data suggest that microwave irradiation may activate endogenous opioids, which in turn alter the actions of psychoactive drugs, and the effect of microwaves on drug action can be classically conditioned.

Amphetamine↗
PubMed1986

Low-level microwave irradiation attenuates naloxone-induced withdrawal syndrome in morphine-dependent rats.

The effect of microwave irradiation on naloxone-induced withdrawal syndrome was studied in rats made morphine dependent by subcutaneous implantation of morphine pellets. Morphine-dependent rats were either exposed to pulsed low-level microwaves (2450 MHz, 1 mW/cm2, 500 pps, 2 musec pulses) or sham-irradiated for 45 min before the naloxone injection. We found that microwave-exposed rats showed significantly less weg-dog-shakes and had higher body temperature than the sham-exposed animals during withdrawal. There was no significant difference in the incident of diarrhea between the two groups of animals. These data further support the results of our previous research suggesting that pulsed low-level microwave irradiation activates endogenous opioids in the rat.

Animals↗
PubMed1986

Decreased muscarinic acetylcholine receptor number in the central nervous system of the tottering (tg/tg) mouse.

The tottering mouse (tg/tg) is a single-locus mutant, phenotypically characterized by the development of epilepsy associated with distinct electroencephalographic abnormalities. Because of reported alterations in muscarinic receptor (mAChR) number in various seizure states, mAChR density was examined in discrete brain regions of tottering (tg/tg) and coisogenic wild-type (+/+) mice. Saturation binding experiments revealed a widespread decrease in membrane mAChR density in the CNS of adult tottering (tg/tg) mice as compared with age-matched control wild-type (+/+) mice. The decrease was most pronounced in the hippocampus, where tg/tg mice exhibited a 40-60% reduction in mAChR density with no change in the affinity of the receptor for antagonists or agonists. At postnatal day 10, before the reported onset of electroencephalographic abnormalities, 114 and 65% increases in mAChR density were observed in the tg/tg hippocampus and cortex, respectively. Following the development of seizure activity at postnatal day 22, mAChR density in the tg/tg hippocampus was reduced by 29%. No change in brain mAChR density was seen in adult heterozygotes (+/tg), which do not develop electroencephalographic or seizure abnormalities. These results indicate that the development of reduced mAChR number in the CNS of the tg/tg mouse is secondary to abnormal neuronal activity, providing further support for the hypothesis that membrane depolarization can cause a decrease in neuronal mAChR density.

Aging↗
PubMed1986

The effect of different treatment modalities on connective tissue attachment.

This study compared the effect of four treatment modalities on connective tissue attachment. Ligature-induced periodontitis was established around the mandibular premolars of five young beagle dogs over 8 weeks. Following a 2-week period without ligatures, a reference dog was sacrificed to estimate the extent and nature of the disease. Three dogs received flap procedures in one mandibular posterior segment, and the six experimental roots were treated with citric acid (pH 1) for 3 minutes; the contralateral mandibular segments received flap procedures and the roots were treated with 4% chlorhexidine gluconate in the Hibiclens preparation for 3 minutes. One segment of the control dog received flap procedures, and the roots were treated with sterile normal saline; the contralateral segment received closed root planning. The experimental dogs were sacrificed 1, 2 and 3 months after treatment. The control dog was sacrificed 3 months postoperatively. One week before sacrifice each dog received a Procion dye injection. At sacrifice the study segments of all four treated dogs were clinically healthy, with no observable differences between the different treatment modalities. Histologically, the 1, and 3-month chlorhexidine, the 3-month saline and 3-month root planed specimens had long junctional epithelial adhesions with little connective tissue attachment. The 2-month chlorhexidine and all citric acid-treated sections showed appreciable amounts of new connective tissue attachment. Some 2-month and 3-month citric acid and 2-month chlorhexidine sections showed cementum over the apical portion of the long junctional epithelium. The frequency of occurrence and the length of cementum overlapping epithelium increased appreciably over time.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Specific absorption rate in rats exposed to 2,450-MHz microwaves under seven exposure conditions.

Both positive and negative biological effects of microwaves on drug actions in rats exposed to 1-mW/cm2, 2,450-MHz microwaves have been reported by several investigators. We conducted dosimetry studies for seven different exposure conditions to determine whether these different results could be due to the rats having been exposed differently. They included anterior and posterior exposures in a circular waveguide, near field, far field with E- or H-field parallel to the long axis of the body and dorsal exposure in a miniature anechoic chamber with E- or H-field parallel to the long axis of the body. The average specific absorption rates (SARs) in the head, tail, and body of the exposed rats were measured by means of a calorimetry system. The local SARs at eight locations in the brain were determined by temperature measurement with Vitek probes. Intensive coupling of energy to the tail when it was exposed parallel to the E-field was shown by thermography. For the same average incident power density, the average SARs in the heads of rats were about two times higher in the circular waveguide than for other exposures. The local SARs in the brain varied for different exposure conditions. Statistical comparisons of SARs under the different exposure conditions are presented.

Animals↗
PubMed1985

Hyperthermia in the rat from handling stress blocked by naltrexone injected into the preoptic-anterior hypothalamus.

Experimental handling and colonic temperature measurement have been shown to cause stress and induce a long-lasting rise in colonic temperature in the rat. This stress-induced hyperthermia was blocked by microinjection of the narcotic antagonist naltrexone into the preoptic-anterior hypothalamus (POAH) of the brain, but was not significantly affected by similar injections into areas of the brain above the POAH. Thus, the stress-induced hyperthermia may be caused by activation of the endogenous opioid mechanism in the POAH.

Animals↗
PubMed1985

Intraseptal morphine potentiates pentobarbital narcosis and hypothermia in the rat.

Morphine injected intraseptally in the amounts of 35 and 70 nmol prolonged pentobarbital-induced narcosis in the rat. Pentobarbital-induced hypothermia was also potentiated by intraseptal injection of 70 nmol of morphine. These effects were antagonized when morphine was injected together with naltrexone (29 nmol). Naltrexone injected by itself into the septum did not significantly affect pentobarbital-narcosis and hypothermia. It is concluded that activation of mu opioid receptors in the septal region could affect the actions of pentobarbital.

Anesthesia↗
PubMed1985

Intraseptal microinjections of substance P and analogs potentiate pentobarbital-induced narcosis and depression of hippocampal cholinergic activity.

Intraseptal microinjection of Substance P (SP) has been shown to depress activity in the septal-hippocampal cholinergic pathway in the rat. Pentobarbital also depresses septal-hippocampal cholinergic activity, and a relationship between this depressed activity and pentobarbital-induced narcosis is suggested by a variety of studies. To examine this relationship further, we microinjected SP and its analogs, [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP and [D-Pro2, D-Trp7,9]-SP, intraseptally in rats pretreated with pentobarbital, and measured the duration of loss of righting reflex and change in choline uptake in hippocampal synaptosomes. The duration of pentobarbital-induced loss of righting reflex was prolonged and the pentobarbital-induced reduction of hippocampal choline uptake was enhanced by all three drugs. A negative correlation (r = -0.96, P less than .02) was seen between duration of loss of righting reflex and synaptosomal choline uptake. Thus, the two analogs of SP appear to act as SP agonists at the septum, judged by their abilities to potentiate pentobarbital narcosis and reduce septal-hippocampal cholinergic activity. This is in contrast to reported actions of these two analogs as SP antagonists in various peripheral tissues.

Animals↗
PubMed1984

Effects of dopaminergic and serotonergic drugs on ethanol-induced hypothermia.

The effects of dopaminergic and serotonergic drugs on ethanol-induced hypothermia were studied in the rat. Pretreatment with haloperidol attenuated the hypothermia in a dose-dependent manner. Apomorphine produced a dose-dependent effect on the hypothermia. At a dose of 2.0 mg/kg, apomorphine potentiated ethanol-induced hypothermia, whereas at 0.1 mg/kg, it produced a delayed attenuation effect between 30 min and 45 min after its injection. The former effect was blocked by haloperidol, whereas the latter was not affected by haloperidol, but blocked by pretreatment with parachlorophenylalanine. It is concluded that both dopamine and serotonin exert modulatory effects on ethanol-induced hypothermia.

Animals↗
PubMed1984

Effects of acute low-level microwaves on pentobarbital-induced hypothermia depend on exposure orientation.

Two series of experiments were performed to study the effects of acute exposure (45 min) to 2,450-MHz circularly polarized, pulsed microwaves [1 mW/cm2, 2-mus pulses, 500 pps, specific absorption rate (SAR) 0.6 W/kg] on the actions of pentobarbital in the rat. In the first experiment, rats were irradiated with microwaves and then immediately injected with pentobarbital. Microwave exposure did not significantly affect the extent of the pentobarbital-induced fall in colonic temperature. However, the rate of recovery from the hypothermia was significantly slower in the microwave-irradiated rats and they also took a significantly longer time to regain their righting reflex. In a second experiment, rats were first anesthetized with pentobarbital and then exposed to microwaves with their heads either pointing toward the source of microwaves (anterior exposure) or pointing away (posterior exposure). Microwave radiation significantly retarded the pentobarbital-induced fall in colonic temperature regardless of the orientation of exposure. However, the recovery from hypothermia was significantly faster in posterior-exposed animals compared to those of the anterior-exposed and sham-irradiated animals. Furthermore, the posterior-exposed rats took a significantly shorter time to regain their righting reflex than both the anterior-exposed and sham-irradiated animals.

Animals↗
PubMed1984

Ethanol-induced hypothermia and ethanol consumption in the rat are affected by low-level microwave irradiation.

Microwave irradiation of rats by circularly polarized, 2,450-MHz, pulsed waves (2-microseconds pulses; 500 pps) was performed in waveguides to determine effects on ethanol-induced hypothermia and on ethanol consumption. Rats injected intraperitoneally with ethanol (3 g/kg in a 25% v/v water solution) immediately after 45 min of microwave irradiation exhibited attenuation of the initial rate of fall in body temperature, which was elicited by the ethanol, but exhibited no significant difference in maximal hypothermia as compared with that of sham-irradiated rats. Microwave irradiation did not affect the consumption of a 10% sucrose (w/v) solution by water-deprived rats. However, it enhanced the consumption of a solution of 10% sucrose (w/v) + 15% ethanol (v/v) by water-deprived animals. These results were obtained at a specific absorption rate (SAR) of 0.6 W/kg, which rate of energy dosing would require a power density of 3-6 mW/cm2 if exposure of the animals had occurred to a 12-cm plane wave.

Alcohol Drinking↗